Insulins are biologic medicines, so once patents expire you might get biosimilar drugs which also require FDA approval, not generics as with other drugs. Admelog is the biosimilar for Humalog, approved by the FDA in early 2018.
As I understand it, Sanofi (Admelog's manufacturer) sets the price to be only slightly below that of Humalog.
Eli Lilly, Novo Nordisk, and Sanofi manufacture substantially all of the insulin, and they more or less follow each other price-wise. There's not the competition you would expect that would drive down prices.
EDIT: they compete by offering varying discounts to particular insurance companies to only cover their insulin at the exclusion of the other company's insulins. This often leads to a letter to patients near the end of the year telling them that the insurance company has decided that their treatment plan has now changed, decisions of their doctor be damned. (Yes, you can appeal and what-not, but it's still fundamentally the insurance company's decision, not your doctor.) This, of course, also screws anyone without insurance who is expected to pay list price.
I totally agree with you regarding drug prices overall, but insulin is different in this respect. A vial of Humalog cost $35 in 2001. The exact same size vial of the exact same insulin -- no refreshed patent, no reformulations, no improvements, no change whatsoever -- cost $270 in 2017. If the price would have only followed inflation, it would have been $48.50 in 2017.
To clarify, the IMMINENT DEATH possibility is also true, in the case of diabetic ketoacidosis, which is caused from lack of insulin. Yes, if it came to it, you could use Walmart's NPH/R to avoid DKA, but then you put yourself at a higher risk of severe hypoglycemia (extreme low blood sugar) due to the way those insulins work, which can also result in imminent death.
My comment previously was referring to the best case, where you only lose some toes or a foot in a decade or two.
This depends on what you mean by "plain insulin". If you are referring to NPH and R, there's a massive world of difference going to, say, Novolog and Lantus. If you're comparing something like Lantus versus Tresiba, sure, it's more "extended release" Or yes, Afrezza is inhalable. But when people complain about the cost of insulin, they're referring to the cost, and especially the huge cost increases, of insulins like Lantus and Novolog (that have been out for a couple decades now), not the cost of new insulins like Afrezza or Tresiba.
Not going to respond on the rest of your comment, but on insulin, I want to rebut the idea that generics are the same as "fancy and more convenient" versions. They are completely different drugs with different (and far worse) clinical outcomes.
You might as well say "infected people won't have amputations like we've been doing forever. They must always have the fancy and more convenient antibiotics instead."
The fact is, because of intrinsic differences in the types of insulin, a regimen of NPH and/or R can not help but have a significant increase in diabetic complications (including amputations, as in my statement above) than a basal/bolus regimen of Lantus/Levemir and Novolog/Humalog -- all of which have been available for something like 20 years and all of which have seen predatory price increases.